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Based on telescopic observations, it is easy to see that the maria (dark regions) on the Moon have far fewer craters than the highlands (bright regions). This led scientists to believe that _____.

Active outflows on Mars are observed in the _____ hemisphere on Mars. The liquid involved is thought to be _____.

Since the average densities of the Moon and Mars are about _____, we conclude that both objects _____.

The channels and outflow features discovered on Mars by Mariner 9 and the Mars Global Surveyor show that _____.

Consider the following list of items:Which of the items on the list were used to discover the high surface temperature of Mercury?

The radius of the Moon is R=1.7 x 108 cm and its mass is M=7.4 x 1025 g. From these values, we conclude that the volume is _____ and the mean density ρ is _____. Hint: the volume V of a sphere of radius R is given by the formula V = (4/3) π R3 and the average density ρ is given by the formula ρ=M/V.

Impact craters on Mercury are generally _____ than impact craters on the Moon _____ because.

The retrograde spin of Venus and the 98 degree tilt of the spin axis of Uranus are thought to be due to _____.

The most common gas in the atmospheres of Mars and Venus is _____. The most common gas in the atmospheres of Jupiter and Saturn is _____.

Venus and Mars have about the same percentage of CO2 in their atmospheres. However, only Venus has a strong greenhouse effect because _____.